1. Field of the Invention
The present invention relates generally to an image sensor used in facsimile apparatus, printing apparatus and the like, and document reading apparatus having such an image sensor, and in particular to an image sensor unit which is easily maintained and reusable.
2. Description of the Related Art
FIG. 4 and FIG. 15 show a conventional image sensor of the type described, for example, in the Proceedings of SPIE (Society of Photo-Optical Instrumentation Engineers), Solid State Sensor Arrays: Development and Applications, Vol. 3019 (February 1997). FIG. 15 is an isometric view and FIG. 4 is a sectional view.
With reference to FIG. 4, an image sensor unit 7 includes a circuit board 2, a linear array of light emitting diodes 3 mounted on the circuit board 2, a rod lens array 4 for forming a 1:1 size image, which is comprised of a plurality of rod lenses (not shown), a linear array of sensor ICs 5 arranged on the circuit board 2, and a glass plate 6 positioned on the surface of the image sensor 7 across which a document 1 to be scanned travels. With reference to FIG. 15, numeral 7a denotes an end surface of the image sensor unit 7 and numeral 8 denotes a pair of tapped holes in end surface 7a used for attaching the image sensor unit to a document reading apparatus, such as a facsimile machine or printer.
In operation, the array of light emitting diodes 3 is arranged on the circuit board 2 as a line light source. The light beam from the light emitting diode array 3 passes through the glass plate 6 and illuminates the document 1, with reflected light from the document 1 (having a pattern corresponding to the density information of an image on the document 1) being transmitted through the rod lenses of the rod lens array 4 and formed as an image onto the sensor IC array 5. The array 5 is formed of a plurality of sensor ICs each a few millimeters long and arranged linearly according to the line reading direction of the image sensor. The ICs accumulate electric charges according to the intensity of the reflected light beam from the document 1, which charges are converted to a voltage signal that is outputted via the circuit board 2.
The frame of the image sensor unit 7 supports the rod lens array 4, the glass plate 6, and the circuit board 2. The circuit board 2 and the glass plate 6 are firmly secured to the frame of the unit 7 by an adhesive or the like such that they are not easily separated from the frame of the unit 7. In this regard, it is desired to prevent foreign matter from infiltrating the image sensor after assembly and possibly interfering with the reflected light beam from document 1 by settling between the glass plate 6 and the rod lens array 4. Consequently, the interior and exterior of the sensor unit 7 are completely isolated from each other by installing the circuit board 2 and the glass plate 6 in a permanent manner.
However, the conventional image sensor unit described above suffers from the problem that if during the manufacturing process foreign matter gets into the area surrounded by the circuit board 2, the glass plate 6, and the frame of the unit 7, and such foreign matter is not discovered until inspection of the unit after assembly, the structure in which the circuit board 2 and the glass plate 6 are firmly secured to the frame of the unit 7 with an adhesive or the like makes it difficult to detach these components from the frame of the unit in order to discharge the foreign matter from the interior with a blast of air or the like. Therefore, it is difficult to disassemble the components for removal of foreign matter, which frequently results in inevitable discarding of such assembled sensor units. Such cases arise even where the foreign matter is not located between the glass plate 6 and the rod lens array 4, because of the opportunity for the foreign matter to travel to that location as a result of subsequent handling of the image sensor unit and/or the document reading apparatus in which it is installed. Thus, even in cases where a foreign substance has infiltrated the sensor unit but is not between the glass plate and the rod lens array, such image sensor units cannot reliably be used in document reading apparatus.
Further, the conventional image sensor unit is installed in the document reading apparatus using screws which are screwed into tapped holes 8. Since it is difficult to directly screw the image sensor unit to the appropriate part of the document apparatus from the standpoint of assembly, a method has been employed wherein a mounting fixture having a shape suited for fixing the image sensor unit to the apparatus is provided and screwed to the image sensor unit, and the image sensor unit is then secured to the apparatus via the mounting fixture. However, securing the image sensor unit to the apparatus via the mounting fixture results in poor image sensor positioning precision within the apparatus. Such poor positioning with respect to the apparatus poses the problem of scanned images being crooked and discontinuous because the document 1 cannot be fed straight with respect to the image sensor unit. There thus exists a need for improvement in the art to eliminate the shortcomings and problems discussed above.
The present invention has been made with a view toward solving the problems mentioned above, and it is thus an object of the invention to provide an image sensor in which it is possible to easily expel foreign substances from an area surrounded by the circuit board 2, the glass plate 6, and the frame of the unit 7, without removing the circuit board 2 or the glass plate 6, thereby obviating the need to discard assembled sensor units containing foreign substances because of difficulty in disassembling and reassembling the components to remove such substances.
It is another object of the invention to provide an image sensor which permits accurate positioning of the image sensor withing document reading apparatus and enables straight and continuous images of scanned documents to be produced.
According to a first aspect of the invention, an image sensor includes a light source for irradiating light onto a document, a photoreceptor for receiving the light reflected by the document, an enclosure which houses the light source and the photoreceptor and having a plurality of wall surfaces which surround the light source and the photoreceptor, at least one of the wall surfaces being provided with a through hole; and
a closing member detachably attached to the wall surface provided with the through hole, the closing member closing the through hole when the closing member is attached to the wall surface provided with the through hole.
Further, the wall surface provided with the through hole having a contact portion and the remaining portion, the contact portion contacting with the closing member, the contact portion being recessed with respect to the remaining portion thereby forming a step between the contact portion and the remaining portion.
The thickness of the closing member is smaller than the height of the step.
A document reading apparatus in accordance with the invention has:
an image sensor having a light source which irradiates light onto a document, a photoreceptor for receiving the light reflected by the document, and an enclosure which houses the light source and the photoreceptor and having a plurality of wall surfaces which surround the light source and the photoreceptor, a through hole being provided in at least one of the wall surfaces;
a rest on which the image sensor is rested; and
a fixing member for securing the image sensor on the rest, the fixing member being provided with a protuberance which fits in the through hole.
The document reading apparatus further has a closing member which comes in contact with the wall surface provided with the through hole to close the through hole, wherein fitting the protuberance in the through hole causes the protuberance to push the closing member against the wall surface provided with the through hole.
A document reading apparatus in accordance with the invention comprises:
an image sensor having a light source which irradiates light onto a document, a photoreceptor for receiving the light reflected by the document, and an enclosure which houses the light source and the photoreceptor and having a plurality of wall surfaces which surround the light source and the photoreceptor, a recessed portion being provided in at least one of the wall surfaces;
a rest on which the image sensor is rested; and
a fixing member for securing the image sensor to the rest, the fixing member being provided with a protuberance which fits in the recessed portion.